Air Pollution as a Climate Forcing: A Workshop

Day 3 Presentations

NOx Controls for the Power Industry

Rui Afonso
Energy and Environmental Strategies for the Clean Air Task Force

With electric generation accounting for approximately 25-35% of
total NOx emissions, NOx reductions in the
central station, power sector will impact ozone and nitrate production.

There are two categories of NOx emission control,
those that minimize the formation of NOx during the
combustion process (e.g., smaller quantities of NOx
are formed), and those that reduce the amount of NOx
formed prior to exiting the stack into the
atmosphere. In industry "language" the first is referred to
under the "umbrella" of Combustion Modifications; technologies
in the second category are termed "Post-Combustion Controls."

Selective Catalytic Reduction (SCR) is a post combustion
technology capable of large NOx reductions (90+%) and
represents at present the most effective NOx control
technology. It uses an ammonia-containing reagent to react with
the NOx produced in the boiler, and converts it to
harmless nitrogen and water. Capital costs range from about $50
to $100/kW. Operating costs are driven primarily by the
consumption of the chemical reagent — usually ammonia.

SCR technology was first used on utility boilers in the 1970s in
Japan, followed by extensive deployment in Japan and Germany in
the mid to late 1980s. By 1990, the number of commercial units
in Japan and Germany had grown to about 200 units or about
40,000 MW of capacity. Most applications in Japan and Germany
were designed to achieve 60%-80% NOx removal
efficiencies. Technical development/assessment activities in the
U.S. geared up at this time as well. In California,
anticipating the requirements of Rule 1135, RECLAIM, etc.,
SCR-related developments for gas-fired applications were
underway. The status of SCR for coal-fired boilers in the U.S.
made a major leap in the mid 1990s when a number of new
coal-fired boilers were permitted and went online using SCR
technology, and technical research and innovation have continued.

In the US, market projections suggest many SCR retrofits over
the next several years to comply with emissions requirements.
For coal-based boilers, it is projected that some additional
80,000 -100,000 MW of SCR capacity will be deployed by 2006-07.
For gas-fired generation (gas turbine combined cycle), the
equivalent projection is about 75,000-80,000 MW of new SCR. This
represents a significant fraction (>30%) of the current
fossil generation capacity in the US.

Today gas-fired generation can achieve NOx emissions
in the single digit (PPM) level. In the next couple of decades,
advanced coal technologies (gasification) will make it possible
to achieve similar results for coal-based generation.